The invention relates to a strain relief mechanism for a tool. In particular, the invention relates to a strain relief mechanism for a plasma arc torch which includes a positive axial restraint component and a positive rotational restraint component.
Plasma arc torches are widely used in the cutting or marking of metallic materials. A plasma torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling and arc control fluids, a swirl ring to control fluid flow patterns in the plasma chamber formed between the electrode and nozzle, and a power supply. The torch produces a plasma arc, which is a constricted ionized jet of a gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g. argon or nitrogen), or reactive (e.g. oxygen or air).
In operation, a pilot arc is first generated between the electrode (cathode) and the nozzle (anode). Generation of the pilot arc may be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or any of a variety of contact starting methods.
One known configuration of a plasma arc torch includes one or more leads connecting the torch to the power supply to provide the torch with electrical current and gas. The connection of the lead(s) to the power supply must be rugged to handle the strain placed on the lead as it is manipulated in order to place the plasma arc torch in a position to cut or mark a workpiece. While most operators of hand-held systems use the plasma arc torch, lead and power supply properly, some operators have used the lead for purposes not intended by the manufacturer (e.g. stepping on the lead(s) or even pulling the lead(s) to drag the power supply to a new location).
The lead(s) used to connect the torch to the power supply can be a single integral lead having a gas hose located in the middle of the lead and electrical conductors and fillers arranged symmetrically around the gas hose. A jacket material is extruded over the gas hose, electrical conductors and fillers. A strain relief mechanism can be attached to the jacket to handle loads applied to the lead. The jacket, gas hose, electrical conductors and fillers are anchored together over a barb-type fitting. A clamp, which acts as the strain relief mechanism, is applied to grab and hold the jacket to prevent relative axial motion (or twisting) of the lead components. The stress through the lead is absorbed by the clamp and transferred to the chassis of the power supply through a mechanical connection.
One example of an integral lead with a clamp which prevents axial motion or twisting of lead components is found in the lead used in the PMX900/PAC125 plasma arc torch system manufactured by Hypertherm, Inc. The lead used in this plasma arc torch system is connected to the power supply by a threaded quick disconnect connector. A quick disconnect connector is advantageous in that it simplifies torch removal but is expensive to make. Another example of an integral lead with a clamp for preventing axial motion (or twisting) of lead components can be found in the lead used in the PMX600/PAC123 plasma arc torch system manufactured by Hypertherm, Inc. In this system, stress is absorbed by the chassis of the power supply through a tool-tightened nut. A tool-tightened nut is advantageous in that it is inexpensive, but the tool-tightened nut requires the use of a tool. The use of a tool can be time consuming, and the tool can be easily misplaced.
It is therefore an object of the present invention to provide an improved and inexpensive axial and rotational strain relief mechanism for connecting a lead to a plasma arc torch power supply.
In one aspect, the invention features a strain relief system for restraining a lead relative to a housing. The strain relief system includes a positive axial restraint component for restraining axial movement of the lead relative to the housing and a positive rotational restraint component for restraining rotational movement of the lead relative to the housing. The positive axial restraint component and the positive rotational restraint component are independent components arranged in a spaced relationship relative to each other. In one embodiment, the positive axial restraint component comprises a quick disconnect connector and the positive rotational restraint component comprises a shaped boot attached to the lead.
In another aspect, the invention features a plasma arc torch for piercing or cutting a workpiece. The plasma arc torch includes a torch body, a power supply, a lead with two ends. The first end of the lead is connected to the torch body, and the second end of the lead is attached to a strain relief system to couple the lead to the power supply. The strain relief system includes a positive axial restraint component for restraining axial movement of the lead relative to the power supply and a positive rotational restraint component for restraining rotational movement of the lead relative to the power supply. The positive axial restraint component and the positive rotational restraint component are independent components arranged in a spaced relationship relative to each other.
In another aspect, the invention features a method for restraining a lead relative to a housing. The method includes the steps of providing a positive axial restraint component for restraining axial movement of the lead relative to the housing, and providing a positive rotational restraint for restraining rotational movement of the lead relative to the housing, and connecting the lead to the housing. The positive axial restraint component and the positive rotational restraint component are independent components arranged in a spaced relationship relative to each other.
In yet another aspect, the invention features a method for restraining a lead relative to a power supply for a plasma arc torch. The method includes the steps of providing a positive axial restraint component for restraining axial movement of the lead relative to the power supply and providing a positive rotational restraint component for restraining rotational movement of the lead relative to the power supply. The positive axial restraint component and the positive rotational restraint component are independent components. The method also includes the step of arranging the positive axial restraint component and the positive rotational restraint component in a spaced relationship relative to each other along a longitudinal axis of the lead. Further, the method includes the step of connecting the lead to the power supply for the plasma arc torch.